Isotopes of americium

Actinides				Half-life	Fission products
²⁴⁴Cm	²⁴¹Pu ^f	²⁵⁰Cf	²⁴³Cm^f	10–30 y	¹³⁷Cs	⁹⁰Sr	⁸⁵Kr
²³²U ^f		²³⁸Pu	f is for fissile	69–90 y			¹⁵¹Sm nc➔
4n	²⁴⁹Cf ^f	²⁴²Am^f	f is for fissile	141–351	No fission product has half-life 10² to 2×10⁵ years
4n	²⁴¹Am		²⁵¹Cf ^f	431–898
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm	²⁴³Am	5–7 ky
4n	²⁴⁵Cm^f	²⁵⁰Cm	²³⁹Pu ^f	8–24 ky
	²³³U ^f	²³⁰Th	²³¹Pa	32–160
	4n+1	²³⁴U	4n+3	211–290	⁹⁹Tc		¹²⁶Sn	⁷⁹Se
²⁴⁸Cm	4n+1	²⁴²Pu		340–373	Long-lived fission products
	²³⁷Np	4n+2		1–2 My	⁹³Zr	¹³⁵Cs nc➔
²³⁶U	4n+1		²⁴⁷Cm^f	6–23 My		¹⁰⁷Pd	¹²⁹I
²⁴⁴Pu				80 My	>7%	>5%	>1%	>.1%
²³²Th		²³⁸U	²³⁵U ^f	0.7–12 Gy	fission product yield

Americium (Am) is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was ²⁴¹Am in 1944.

19 radioisotopes of americium have been characterized, with the most stable being ²⁴³Am with a half-life of 7,370 years, and ²⁴¹Am with a half-life of 432.7 years. All of the remaining radioactive isotopes have half-lives that are less than 51 hours, and the majority of these have half-lives that are less than 100 minutes. This element also has 8 meta states, with the most stable being ^242mAm (t_½ 141 years). The isotopes of americium range in atomic weight from 231.046 u (²³¹Am) to 249.078 u (²⁴⁹Am).

1 Some notable isotopes
2 Table
- 2.1 Notes
3 See also
4 References

Some notable isotopes

Americium-241

Americium-241 is the most prevalent isotope of americium in nuclear waste.^[1] It is the americium isotope used in an americium smoke detector based an ionization chamber. It is a potential fuel for long-lifetime radioisotope thermoelectric generators.

Parameter	Value
Atomic mass	241.056823 u
Mass excess	52930 keV
Beta decay energy	-767 keV
Spin	5/2-
Half-life	432.2 years
Spontaneous fissions	1200 per kg/s
Decay heat	114 watts/kg

Possible parent nuclides: beta from ²⁴¹Pu, electron capture from ²⁴¹Cm, alpha from ²⁴⁵Bk.

Americium-241 decays by alpha emission, with a by-product of gamma rays. Its presence in plutonium is determined by the original concentration of plutonium-241 and the sample age. Because of the low penetration of alpha radiation, Americium-241 only poses a health risk when ingested or inhaled. Older samples of plutonium containing plutonium-241 contain a buildup of ²⁴¹Am. A chemical removal of americium from reworked plutonium, e.g. during reworking of plutonium pits, may be required.

Americium-242m

^242mAm decay modes (halflife: 141 years)
Probability	Decay mode	Decay energy	Decay product
99.54%	isomeric transition	0.05 MeV	²⁴²Am
0.46%	alpha decay	5.64 MeV	²³⁸Np
(1.5±0.6)×10⁻¹⁰^[3]	spontaneous fission	~200 MeV	fission products

Americium-242m has a mass of 242.0595492 g/mol. It is one of the rare cases, like ^180mTa, where a higher-energy nuclear isomer is more stable than the lower-energy one, Americium-242.^[4]

^242mAm is fissile (because it has an odd number of neutrons) and has a low critical mass, comparable to that of ²³⁹Pu.^[5] It has a very high cross section for fission, and if in a nuclear reactor is destroyed relatively quickly. Another report claims that ^242mAm has a much lower critical mass, can sustain a chain reaction even as a thin film, and could be used for a novel type of nuclear rocket.^[6]

²⁴²Am decay modes (halflife: 16 hours)
Probability	Decay mode	Decay energy	Decay product
82.70%	beta decay	0.665 MeV	²⁴²Cm
17.30%	electron capture	0.751 MeV	²⁴²Pu

Americium-243

Americium-243 has a mass of 243.06138 g/mol and a half-life of 7,370 years, the longest lasting of all americium isotopes. It is formed in the nuclear fuel cycle by neutron capture on plutonium-242 followed by beta decay.^[7] Production increases exponentially with increasing burnup as a total of 5 neutron captures on ²³⁸U are required.

It decays by either emitting an alpha particle (with a decay energy of 5.27MeV)^[7] to become ²³⁹Np, which then quickly decays to ²³⁹Pu, or infrequently, by spontaneous fission.^[8]

²⁴³Am is a hazardous substance, because it can cause cancer. ²³⁹Np, which is formed from ²⁴³Am, emits dangerous gamma rays, making ²⁴³Am the most dangerous isotope of Americium.^[1]

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)^[9]^{[n 1]}	daughter isotope(s)	nuclear spin
nuclide symbol	excitation energy			half-life	decay mode(s)^[9]^{[n 1]}	daughter isotope(s)	nuclear spin
²³¹Am	95	136	231.04556(32)#	30# s	β⁺	²³¹Pu
²³¹Am	95	136	231.04556(32)#	30# s	α (rare)	²²⁷Np
²³²Am	95	137	232.04659(32)#	79(2) s	β⁺ (98%)	²³²Pu
					α (2%)	²²⁸Np
					β⁺, SF (.069%)	(various)
²³³Am	95	138	233.04635(11)#	3.2(8) min	β⁺	²³³Pu
²³³Am	95	138	233.04635(11)#	3.2(8) min	α	²²⁹Np
²³⁴Am	95	139	234.04781(22)#	2.32(8) min	β⁺ (99.95%)	²³⁴Pu
					α (.04%)	²³⁰Np
					β⁺, SF (.0066%)	(various)
²³⁵Am	95	140	235.04795(13)#	9.9(5) min	β⁺	²³⁵Pu	5/2-#
²³⁵Am	95	140	235.04795(13)#	9.9(5) min	α (rare)	²³¹Np	5/2-#
²³⁶Am	95	141	236.04958(11)#	3.6(1) min	β⁺	²³⁶Pu
²³⁶Am	95	141	236.04958(11)#	3.6(1) min	α	²³²Np
²³⁷Am	95	142	237.05000(6)#	73.0(10) min	β⁺ (99.97%)	²³⁷Pu	5/2(-)
²³⁷Am	95	142	237.05000(6)#	73.0(10) min	α (.025%)	²³³Np	5/2(-)
²³⁸Am	95	143	238.05198(5)	98(2) min	β⁺	²³⁸Pu	1+
²³⁸Am	95	143	238.05198(5)	98(2) min	α (10⁻⁴%)	²³⁴Np	1+
^238mAm	2500(200)# keV			35(10) µs
²³⁹Am	95	144	239.0530245(26)	11.9(1) h	EC (99.99%)	²³⁶Pu	(5/2)-
²³⁹Am	95	144	239.0530245(26)	11.9(1) h	α (.01%)	²³⁵Np	(5/2)-
^239mAm	2500(200) keV			163(12) ns			(7/2+)
²⁴⁰Am	95	145	240.055300(15)	50.8(3) h	β⁺	²⁴⁰Pu	(3-)
²⁴⁰Am	95	145	240.055300(15)	50.8(3) h	α (1.9×10⁻⁴%)	²³⁶Np	(3-)
²⁴¹Am^{[n 2]}	95	146	241.0568291(20)	432.2(7) a	α	²³⁷Np	5/2-
					CD (7.4×10⁻¹⁰%)	²⁰⁷Tl, ³⁴Si
					SF (4.3×10⁻¹⁰%)	(various)
^241mAm	2200(100) keV			1.2(3) µs
²⁴²Am	95	147	242.0595492(20)	16.02(2) h	β^- (82.7%)	²⁴²Cm	1-
²⁴²Am	95	147	242.0595492(20)	16.02(2) h	EC (17.3%)	²⁴²Pu	1-
^242m1Am	48.60(5) keV			141(2) a	IT (99.54%)	²⁴²Am	5-
					α (.46%)	²³⁸Np
					SF (1.5×10⁻⁸%)	(various)
^242m2Am	2200(80) keV			14.0(10) ms			(2+,3-)
²⁴³Am^{[n 2]}	95	148	243.0613811(25)	7,370(40) a	α	²³⁹Np	5/2-
²⁴³Am^{[n 2]}	95	148	243.0613811(25)	7,370(40) a	SF (3.7×10⁻⁹%)	(various)	5/2-
²⁴⁴Am	95	149	244.0642848(22)	10.1(1) h	β^-	²⁴⁴Cm	(6-)#
^244mAm	86.1(10) keV			26(1) min	β^- (99.96%)	²⁴⁴Cm	1+
^244mAm	86.1(10) keV			26(1) min	EC (.0361%)	²⁴⁴Pu	1+
²⁴⁵Am	95	150	245.066452(4)	2.05(1) h	β^-	²⁴⁵Cm	(5/2)+
²⁴⁶Am	95	151	246.069775(20)	39(3) min	β^-	²⁴⁶Cm	(7-)
^246m1Am	30(10) keV			25.0(2) min	β^- (99.99%)	²⁴⁶Cm	2(-)
^246m1Am	30(10) keV			25.0(2) min	IT (.01%)	²⁴⁶Am	2(-)
^246m2Am	~2000 keV			73(10) µs
²⁴⁷Am	95	152	247.07209(11)#	23.0(13) min	β^-	²⁴⁷Cm	(5/2)#
²⁴⁸Am	95	153	248.07575(22)#	3# min	β^-	²⁴⁸Cm
²⁴⁹Am	95	154	249.07848(32)#	1# min	β^-	²⁴⁹Cm

^ Abbreviations:
CD: Cluster decay
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission
^ ^a ^b Most common isotopes

Notes

Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses - ( ).
Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References

^ ^a ^b "Americium". Argonne National Laboratory, EVS. Retrieved 25 December 2009.
^ Sasahara, Akihiro; Matsumura, Tetsuo; Nicolaou, Giorgos; Papaioannou, Dimitri (April 2004). "Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO2 and MOX Spent Fuels". Journal of NUCLEAR SCIENCE and TECHNOLOGY 41 (4): 448–456. doi:10.3327/jnst.41.448. http://www.jstage.jst.go.jp/article/jnst/41/4/448/_pdf.
^ Phys. Rev. 155 (1967): J. T. Caldwell, S. C. Fultz, C. D. Bowman, and R. W. Hoff - Spontaneous Fission Half-Life of 242mAm (halflife (9.5±3.5)×10¹¹
^ 95-Am-242
^ http://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf
^ Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks
^ ^a ^b "Americium-243". Oak Ridge National Laboratory. Retrieved 25 December 2009.
^ "Isotopes of the Element Americium". Jefferson Lab Science Education. Retrieved 25 December 2009.
^ http://www.nucleonica.net/unc.aspx

Isotope masses from:
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.
Isotopic compositions and standard atomic masses from:
- J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry 75 (6): 683–800. doi:10.1351/pac200375060683. http://www.iupac.org/publications/pac/75/6/0683/pdf/.
- M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry 78 (11): 2051–2066. doi:10.1351/pac200678112051. http://iupac.org/publications/pac/78/11/2051/pdf/. Lay summary.
Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.
- National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. http://www.nndc.bnl.gov/nudat2/. Retrieved September 2005.
- N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0849304859.

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